It is frequently said that the world has entered an information era. Huge quantities of information are already being transmitted through extensive electronic networks on an almost instantaneous basis to satisfy voracious appetites of businesses and individuals for knowledge. There is nothing that indicates that those appetites will stabilize or diminish in the near future. The expectation is that they will grow stronger.
The information that flows through such networks can, of course, be classified in many ways. One possible classification has to do with whether the information can safely be delayed as it passes through the network. Real time information, including voice or video information, is information that cannot readily be delayed in transit without degrading the quality of the information presented to an end user at an ultimate destination. Non-real time information, including digital data representing alphanumeric or graphical information, is information that can be delayed without necessarily degrading the quality of the information presented to an end user at the destination.
For purposes of convenience, real time information will be identified as voice information or just voice. Non-real time information will be referred to as data. It should be recognized that the word "data" is not being used in its most generic sense; that is, to represent any kind of information in any form. For purposes of this description, the term is limited to non-real time information, usually representing alphanumeric information. It should also be recognized that both voice and data can be encoded using known digital encoding techniques and can be transmitted through digital communication networks.
While voice information is delay intolerant, it is fault tolerant. That is, bit errors introduced as the voice information is being transmitted through the network may not have a significant effect on reproduction quality when the voice information reaches its destination. Data, on the other hand, while delay tolerant, is fault intolerant. Bit errors introduced as the data is being transmitted through the network may result in the data being so corrupted as to be unusable at its destination.
Because voice and data place different demands on communications networks, different kinds of networks have typically been used to transmit the two types of information.
One kind of network that has been developed, primarily for transfer of data between end users, is a frame relay network. In a frame relay network, data is segmented into discrete units or packets which are transmitted in succession along a selected data path through the network. At the receiving end of the data path, the packets are combined to reproduce the data stream which entered the network at the transmitting end. In frame relay systems, the throughput of the system is increased by performing relatively little error checking at the intermediate nodes. If extensive error checking is to be performed, it is performed at the destination.
Data frame relay systems follow protocols established by international standards, such as current ANSI standards T1.617 and T1.618 and CCITT Recommendations Q.922 and Q.933. Systems which follow such standards are optimized for handling of data. Voice information, with its different characteristics and requirements, cannot adequately be supported in data frame relay systems, as presently implemented.